1. Field of the Invention
The present invention relates to a substrate treatment apparatus and a substrate treatment method for removing foreign matter from a surface of a substrate by scrubbing the substrate surface. Exemplary substrates to be treated include semiconductor wafers, glass substrates for liquid crystal display devices, glass substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, and substrates for photo masks.
2. Description of Related Art
In a semiconductor device production process, it is indispensable to perform a substrate cleaning operation between process steps for cleaning a substrate (semiconductor wafer). Substrate treatment apparatuses of a single substrate treatment type which are adapted to clean substrates one by one typically include a substrate holding/rotating mechanism for generally horizontally holding and rotating a substrate, a sponge-like scrub brush for scrubbing a surface of the substrate held and rotated by the substrate holding/rotating mechanism, and a treatment liquid nozzle for supplying a cleaning agent (ammonia water or an ammonia-hydrogen peroxide mixture) to the substrate held and rotated by the substrate holding/rotating mechanism.
The scrub brush is attached to a distal end of a pivot arm, for example, which is horizontally pivotal about a pivot axis located outside a substrate rotation region. When the pivot arm is driven with the scrub brush pressed against the surface of the rotating substrate, the substrate surface is scanned with the scrub brush thereby to be scrubbed. Thus, foreign matter can be removed from the entire substrate surface.
As the scrub-cleaning operation is performed on a multiplicity of substrates, foreign matter on the substrates is transferred to the scrub brush and accumulated in the scrub brush. For suppression of the accumulation of the foreign matter, a scrub brush rinsing operation for rinsing the scrub brush with water is performed in a standby period when no substrate is loaded for treatment for a relatively long period. More specifically, a scrub brush standby position is defined outside the substrate rotation region, and a cleaning pot is provided in the standby position (see, for example, U.S. Pat. No. 5,647,083). The cleaning pot is a tubular container which is capable of accommodating the scrub brush. A deionized water nozzle for supplying deionized water to the scrub brush is provided in the cleaning pot, and a drain pipe is connected to a bottom of the cleaning pot. With this arrangement, the deionized water is supplied from the deionized water nozzle to the scrub brush to wash away the foreign matter from the scrub brush in the standby period.
However, studies conducted by the inventors of the present invention unexpectedly show that a greater amount of foreign matter (particles) apparently remains on a substrate treated by the scrub brush for the first time after the scrub brush is subjected to the rinsing operation in the standby period (the first substrate) than on a substrate subsequently treated by the scrub brush (the second or subsequent substrate).
This phenomenon is supposedly attributable to a change in the zeta potential of the foreign matter adhering to the scrub brush.
The substrate (semiconductor wafer) generally has a negative zeta potential. Therefore, it is effective to cause the foreign matter to have a negative zeta potential for easy removal of the foreign matter from the substrate. For this purpose, ammonia water or an ammonia-hydrogen peroxide mixture is supplied as the cleaning agent to the substrate surface in the scrub-cleaning operation.
However, the surface of the scrub brush supplied with the deionized water in the cleaning pot is liable to have a lower pH. When the scrub brush having a lower pH is pressed against the substrate surface, foreign matter brought into contact with the scrub brush has a positive zeta potential. This supposedly makes it difficult to remove the foreign matter from the substrate surface. When the scrub-cleaning operation is thereafter repeated by supplying the alkaline cleaning agent, the scrub brush abundantly absorbs the alkaline cleaning agent. Therefore, the aforesaid phenomenon is eliminated.
This is supposedly a mechanism that causes the apparent cleaning failure on the first substrate after the standby period.